Effects of Management Practices on Grassland Birds:

Sedge Wren

This report is one in a series of literature syntheses on North American grassland birds. The need for these reports was identified by the Prairie Pothole Joint Venture (PPJV), a part of the North American Waterfowl Management Plan. The PPJV adopted the goal to stabilize or increase populations of declining grassland- and wetland-associated wildlife species in the Prairie Pothole Region. To further that objective, it is essential to understand the habitat needs of birds other than waterfowl, and how management practices affect their habitats. The focus of these reports is on management of breeding habitat, particularly in the northern Great Plains.

Organization and Features of this Species Account

Information on the habitat requirements and effects of habitat management on grassland birds were
summarized from information in more than 5,500 published and unpublished papers. A range map is
provided to indicate the relative densities of the species in North America, based on Breeding
Bird Survey (BBS) data. Although birds frequently are observed outside the breeding range
indicated, the maps are intended to show areas where managers might concentrate their attention.
It may be ineffectual to manage habitat at a site for a species that rarely occurs in an area.
The species account begins with a brief capsule statement, which provides the fundamental components
or keys to management for the species. A section on breeding range outlines the current breeding
distribution of the species in North America, including areas that could not be mapped using BBS data.
The suitable habitat section describes the breeding habitat and occasionally microhabitat
characteristics of the species, especially those habitats that occur in the Great Plains.
Details on habitat and microhabitat requirements often provide clues to how a species will
respond to a particular management practice. A table near the end of the account complements
the section on suitable habitat, and lists the specific habitat characteristics for the species
by individual studies. A special section on prey habitat is included for those predatory
species that have more specific prey requirements. The area requirements section provides
details on territory and home range sizes, minimum area requirements, and the effects of patch
size, edges, and other landscape and habitat features on abundance and productivity. It may be
futile to manage a small block of suitable habitat for a species that has minimum area requirements
that are larger than the area being managed. The Brown-headed Cowbird (Molothrus ater) is an
obligate brood parasite of many grassland birds. The section on cowbird brood parasitism summarizes
rates of cowbird parasitism, host responses to parasitism, and factors that influence parasitism,
such as nest concealment and host density. The impact of management depends, in part, upon a species'
nesting phenology and biology. The section on breeding-season phenology and site fidelity includes
details on spring arrival and fall departure for migratory populations in the Great Plains, peak
breeding periods, the tendency to renest after nest failure or success, and the propensity to
return to a previous breeding site. The duration and timing of breeding varies among regions and
years. Species' response to management summarizes the current knowledge and major findings in the
literature on the effects of different management practices on the species. The section on management
recommendations complements the previous section and summarizes specific recommendations for habitat
management provided in the literature. If management recommendations differ in different portions of
the species' breeding range, recommendations are given separately by region. The literature cited
contains references to published and unpublished literature on the management effects and habitat
requirements of the species. This section is not meant to be a complete bibliography; for a searchable, annotated bibliography of published and unpublished papers dealing with habitat needs of grassland birds and their responses to habitat management, use the Grassland and Wetland Birds Bibliography on the home page of this resource.

Figure. Breeding distribution of the Sedge Wren in the United States and southern Canada, based on Breeding
Bird Survey data, 1985-1991. Scale represents average number of individuals detected per route per year. Map from Price, J., S. Droege, and A. Price. 1995. The summer atlas of North American birds. Academic Press, London, England. 364 pages. (Note: The Breeding Bird Survey may be conducted too early in the southern Great Plains to detect late-season nesting of Sedge Wrens [see Bedell 1996].)

Keys to management include providing tall, dense grassland with moderate forb cover and
minimizing disturbances during the breeding season.

Breeding Range:

Sedge Wrens breed from eastern Saskatchewan through southern Manitoba and southern
Ontario to southern Maine and New Brunswick, south from northeastern Montana and central
North Dakota, through eastern South Dakota, to eastern Kansas and eastern Oklahoma,
and east to New Jersey, Rhode Island, and New Hampshire (National Geographic Society
1987). (See figure for the relative densities of Sedge Wrens in the United States
and southern Canada, based on Breeding Bird Survey data.)

Annual precipitation may affect the occurrence of Sedge Wrens and their habitat use.
Sedge Wrens typically were found in sedge meadows in Wisconsin and Minnesota, but during
dry years they used hayfields, grasslands, and oldfields (Faanes 1981). In North Dakota
during wet years, Sedge Wrens used upland grasslands (Johnson 1997). Presence of breeding
Sedge Wrens in Nebraska and Kansas may be related to years of high precipitation (Tordoff
and Young 1951, Cink 1973, Bedell 1987). During such years, Sedge Wren nests have been
located in short (30 cm) grass with standing water (2 cm), in wetlands, shortgrass prairie, and
along dry hillsides. In southeastern Saskatchewan and southwestern Manitoba, Sedge Wrens
were less common in dry years than in wet years, and used wet meadows during the latter
(Knapton 1979). In Kansas, Sedge Wrens were not present during drought years
(Zimmerman 1993). A table near the end of the account lists the specific habitat
characteristics for Sedge Wrens by study.

Area requirements:

In Illinois native and restored prairies and tame grasslands, area was not as important
as vegetation structure in predicting Sedge Wren occurrence; Sedge Wrens were present on
tallgrass prairie <10 ha (Herkert 1991b, 1994a). When restricting analyses to Sedge Wren
density within just tallgrass prairie fragments, density was positively correlated to area
(Herkert 1994b). In the northern Great Plains (North Dakota, South Dakota, and Minnesota),
Sedge Wrens favored large areas of contiguous grassland habitat over small grassland patches
(D. H. Johnson, unpublished data). In a Minnesota sedge meadow, average territory size was
0.2 ha (Burns 1982). In an Illinois burned prairie, Sedge Wren pairs required 3.4 ha of burned
prairie to establish territories (Schramm et al. 1986).

Brown-headed Cowbird brood parasitism:

No known records of brood parasitism by Brown-headed Cowbirds (Molothrus ater) exist.

Breeding-season phenology and site fidelity:

In the northern Great Plains (North Dakota, Minnesota, and Manitoba), the breeding
season of the Sedge Wren extends from late April to early October (Mousley 1934,
Walkinshaw 1935, Bent 1964, Stewart 1975, Knapton 1979, Faanes 1981), making it one of
the latest-nesting grassland birds. In North Dakota, the peak breeding season is mid-June to
early August (Stewart 1975). In the central and southern Great Plains (Illinois, Iowa, Kansas,
Missouri, and Nebraska), Sedge Wrens may not initiate breeding until July or August
(Schwilling 1982, Skinner et al. 1984, Schramm et al. 1986, Bedell 1987, Lingle and Bedell
1989, Zimmerman 1993, Kent and Dinsmore 1996). One possible explanation for late
breeding attempts is that Sedge Wrens from northern areas may move to southern areas and
raise a second brood because of the longer nesting season (Bedell 1996). Sedge Wrens
migrate through Kansas during late April and early May, only to return in July to breed during
years of normal precipitation levels (Zimmerman 1993). In Minnesota, Sedge Wrens were
double-brooded (Burns 1982).

Species' response to management:

Spring burning in tallgrass prairie can improve habitat by increasing vegetation height
and density and decreasing litter (Eddleman 1974, Schramm et al. 1986). In westcentral
Illinois, Sedge Wrens preferred nesting and foraging in spring-burned areas, yet relied on
unburned areas as a source of litter for nest building (Schramm et al. 1986). In northeastern
and eastcentral Illinois, Sedge Wrens showed no significant response to prescribed burning,
although they did not use a spring-burned prairie fragment of 650 ha 1 yr postburn and were
absent in small (1.4-32 ha) prairie fragments 1-3 yr postburn (Herkert 1991a, 1994b).
However, these results probably were influenced by climatic factors; the first two years of the
study were excessively dry and the third year was abnormally wet. In Illinois Greater
Prairie-Chicken (Tympanuchus cupido) sanctuaries, Sedge Wrens preferred burned areas 3 yr
postburn over hayed and idle areas (Westemeier and Buhnerkempe 1983). In North Dakota,
Sedge Wren occurrence appeared to be unrelated to number of years since last burn, other
than a reduction 1 yr postburn (Johnson 1997). In Nebraska, Sedge Wrens avoided recently
burned CRP fields (Delisle and Savidge 1997). During years of normal precipitation in
Kansas, Sedge Wrens breed in unburned prairie, as well as prairie burned earlier in the
breeding season; during drought years, they may not breed regardless of burn treatment
(Zimmerman 1993). In Missouri, Nebraska, and Wisconsin, Sedge Wrens were present by
July or August on tallgrass prairies burned in the spring of the same year (Skinner et al. 1984,
King 1991, Volkert 1992). Likewise in North Dakota, Sedge Wrens were present in July on a
mixed-grass prairie burned in the spring of the same year (Higgins et al. 1984). In a Kansas study
of spring-burned and unburned native CRP fields, abundance of Sedge Wrens was nonsignificantly higher
on unburned than spring-burned CRP fields (Robel et al. 1998).

In the Midwest (Wisconsin, Iowa, Missouri), Sedge Wrens preferred hayfields that
were dense, lush, and unmown (Skinner 1975, Sample 1989, Frawley and Best 1991). Sedge
Wrens did not use hayfields after the hayfields were mowed (Skinner 1975, Frawley and Best
1991, Herkert 1991a, Delisle and Savidge 1997). In Iowa, Sedge Wrens nested in grassed
waterways that were not mowed the previous year (Bryan and Best 1994). In North Dakota, Sedge
Wrens were significantly more abundant in the year after mowing in idled portions of CRP fields
than in mowed portions (Horn and Koford 2000). During one year of the two-year study, they
were present only in idled portions of CRP fields and not in mowed portions.

Throughout their breeding range, Sedge Wrens avoid areas where vegetation is <10 cm in
height, or where vegetation density has been reduced by moderate to heavy grazing
(Skinner 1974, 1975; Kantrud 1981; Messmer 1985; Lingle and Bedell 1989).
In Missouri, Sedge Wrens preferred lightly grazed areas where vegetation height
was >30.4 cm, followed by idle grasslands and moderately grazed fields where
vegetation height was 20.3-30.4 cm (Skinner 1975). In North Dakota, Sedge Wrens
were more abundant in idle areas than in pastures under season-long or twice-over
grazing systems (Messmer 1990). In southwestern Wisconsin, Sedge Wrens were more
abundant in rotationally grazed pastures than in continuously grazed pastures or
in ungrazed pastures (Temple et al. 1999). Ungrazed grasslands were neither mowed
or grazed from 15 May to 1 July. Continuously grazed sites were grazed throughout
the summer at levels of 2.5-4 animals/ha. Rotationally grazed pastures, stocked
with 40-60 animals/ha, were grazed for 1-2 d and then left undisturbed for 10-15 d
before being grazed again; pastures averaged 5 ha. All sites were composed of 50-75%
cool-season grasses, 7-27% legumes, and 8-23% forbs.

In North Dakota, Sedge Wren density was significantly higher in DNC than in either
idle or grazed native prairie (Renken and Dinsmore 1987). DNC habitat was characterized by
high grass and litter cover, moderate forb cover, low shrub cover, and low amounts of bare
ground. In Saskatchewan, Sedge Wrens preferred DNC (tame or native not specified) to idle
native grasslands or wheat fields (Hartley 1994). In Manitoba, Sedge Wren abundance was
higher in native DNC and tame DNC than in idle native grasslands; productivity was higher in
native DNC than in idle grasslands, but not significantly higher than in tame DNC (Dhol et al.
1994, Jones 1994). In Alberta, Sedge Wrens were found in 3-4 yr old tame DNC fields, but
their numbers were very low (Prescott and Murphy 1999).

In eastcentral Wisconsin, Sedge Wrens gradually increased in subsequent years
following the restoration of a tallgrass prairie (Volkert 1992). Sedge Wrens also were found
on restored tallgrass prairies in Illinois and Kansas (Westemeier and Buhnerkempe 1983,
Schramm et al. 1986, Cink and Lowther 1989). In North Dakota, Sedge Wrens were the
most common species within fields seeded to native grasses (Higgins et al. 1984). In South
Dakota, Sedge Wrens were attracted to rank, dense growth of green needlegrass (Stipa
viridula) in restored fields, which had formerly been cornfields and soybean fields, 2-4 yr
after being seeded to prairie grasses (Blankespoor 1980).

In studies of bird use of cropland in the Great Plains (Illinois, Iowa, Kansas,
Manitoba, Minnesota, Missouri, Montana, Nebraska, North Dakota, Saskatchewan, and
South Dakota), Sedge Wrens were not found in cropland (Patterson and Best 1991, Johnson
and Schwartz 1993b, Hartley 1994, Jones 1994, Johnson and Igl 1995, Best et al. 1997). In
a Saskatchewan study comparing bird use of uplands and wetlands in conventional, minimum-tillage,
and organic farmland and DNC, Sedge Wrens were present only in organic farmland and DNC in
uplands (Shutler et al. 2000). They were more abundant in organic farmland than in DNC. In
Arkansas, Sedge Wrens nested in flooded rice fields when plant height reached 50 cm
(Meanley 1952).

Wetlands that have been modified for waterfowl production are commonly used by Sedge
Wrens (Brady 1983). In eastern South Dakota, Sedge Wrens were found on dug-brood
complexes (a system of channels, ponds, and created islands constructed in wetlands
to provide deep, open water and upland nesting areas for waterfowl). Sedge Wren
densities were higher in the dug-brood complexes than in unmodified wetlands.

Minimize disturbance, such as mowing or herbicide spraying, during the breeding season
(Sample 1989, Frawley and Best 1991, Herkert 1994a, Patterson and Best 1996, Delisle and
Savidge 1997). Because Sedge Wrens have such a long nesting season, delay mowing even
longer than the date generally recommended for other passerines of 15 July. Spray noxious
weeds on a spot-by-spot basis, rather than on an entire-field basis (Delisle and Savidge 1997).

In tallgrass prairie, create a mosaic of burned and unburned areas to provide for both nesting
and foraging needs of the Sedge Wren (Schramm et al. 1986, Volkert 1992).

In Missouri, a rotational system of two or more grazing units may be most beneficial in
providing distinct stands of grasses of various heights, but warm-season grasses should not be
grazed <25 cm (Skinner 1975).

Table. Sedge Wren habitat characteristics.

Author(s)

Location(s)

Habitat(s) Studied*

Species-specific Habitat Characteristics

Bedell 1987

Nebraska

Idle, idle tallgrass, wetland,
wet meadow

Used tall (1.2-1.5 m) wetland vegetation in a complex of
dry wetlands and short grasses; used short grass (≤30
cm) in standing water (2 cm); also were found in
bluestem (Andropogon) prairie adjacent to wetlands

Occurrence was positively related to the percent of wetland area composed of wet-meadow vegetation, to the percent of wetland area within a wetland complex composed of wet-meadow vegetation, and to the area of temporary wetlands within a 3-km buffer around each wetland complex; complexes were defined as tracts of land containing from 4 to 15 wetlands ranging from 44 to 144 ha

Were most abundant on large prairie fragments 2 yr
postburn, and absent from large prairies 1 yr postburn,
small burned prairies, and tame hayland; were
moderately tolerant to fragmentation. Univariate
analysis: density was significantly and positively
correlated to average grass height, average number of
live grass contacts, and total number of contacts of live
grasses, forbs, and residual vegetation; density was
significantly and negatively correlated to percent live
contacts. Multivariate analysis: density was significantly
and positively correlated to total vegetation richness and
vegetation heterogeneity

Herkert 1991b

Illinois

Idle seeded-native, idle
tallgrass, idle tame

Were present on areas <10 ha

Herkert 1994a

Illinois

Idle seeded-native, idle
tallgrass, idle tame

Positive predictors of occurrence were high average
number of contacts of grass, forb, and dead plant
material, and high variability in litter depth, vegetation
height and vegetation density; negative predictor was
average vegetation height; were unaffected by field size

Higgins et al. 1984

North Dakota

Idle seeded-native

Were found in restored native prairie consisting of
western wheatgrass and green needlegrass

Horn and Koford 2000

North Dakota

CRP (idle tame, tame hayland)

Were significantly more abundant in the year after mowing in idled portions of CRP fields than in mowed portions

Johnson and Igl 1995

North Dakota

Cropland, CRP (idle seeded-native, idle tame)

Were found in CRP but not in cropland

Johnson and Schwartz
1993a,b

Minnesota,
Montana,
North Dakota,
South Dakota

Cropland, CRP (idle seeded-native, idle tame)

Density was positively associated with percent grass
cover; were not found in cropland

* In an effort to standardize terminology among studies, various descriptors were used to denote
the management or type of habitat. "Idle" used as a modifier (e.g., idle tallgrass) denotes
undisturbed or unmanaged (e.g., not burned, mowed, or grazed) areas. "Idle" by itself denotes
unmanaged areas in which the plant species were not mentioned. Examples of "idle" habitats include
weedy or fallow areas (e.g., oldfields), fencerows, grassed waterways, terraces, ditches, and road
rights-of-way. "Tame" denotes introduced plant species (e.g., smooth brome [Bromus inermis]) that
are not native to North American prairies. "Hayland" refers to any habitat that was mowed, regardless
of whether the resulting cut vegetation was removed. "Burned" includes habitats that were burned
intentionally or accidentally or those burned by natural forces (e.g., lightning). In situations
where there are two or more descriptors (e.g., idle tame hayland), the first descriptor modifies the
following descriptors. For example, idle tame hayland is habitat that is usually mowed annually but
happened to be undisturbed during the year of the study.